1. Field of the Invention
The present invention relates generally to positioning devices, and more particularly to a device for rotatably positioning a camera about two orthogonal rotational axes.
2. Description of the Prior Art
Videoconferencing systems utilize video cameras to capture an image of the conference participants for transmission to a remote conferencing site. The video camera may be beneficially provided with a device for adjusting the rotational orientation of the camera such that the image of a speaking conference participant is properly framed. The rotational orientation of the camera may be adjusted manually by user manipulation of controls (located either on a videoconferencing system console or on a remote control device associated therewith) which cause the camera to rotate in the desired direction or directions. Alternatively and preferably, adjustment of the camera's rotational orientation is achieved by an automatic technique such as acoustic localization, wherein the position of the speaking participant is calculated by analysis of plural acoustic signals, and the camera is steered in the direction of the calculated position.
Irrespective of whether the camera rotational positioning device is controlled by manual or automatic techniques, such devices require one or more actuators to rotate the camera such that the desired rotational orientation is achieved. Positioning devices designed to rotate the camera about two orthogonal axes (in order to enable more accurate framing of the image of speaking conference participants) typically utilize two actuators: the first actuator rotates the camera about a vertical axis, while the second actuator rotates the camera about a horizontal axis perpendicular to the camera's longitudinal axis. Rotation of the camera about the vertical axis is referred to herein as “panning”; rotation about the horizontal axis is referred to herein as “tilting”; and, devices for rotating the camera about a vertical and horizontal axis are referred to herein as “pan/tilt positioning devices.”
Most presently-employed pan/tilt positioning devices utilize stepper motors to effect rotation of the camera. Stepper motors have the advantage of being relatively inexpensive, easy to control, and widely commercially available in a range of sizes and operational specifications. However, the use of stepper motors to rotate a camera in a videoconferencing system has a number of problems associated therewith. Typically, a gear train or similar set of transmission elements must be employed to transmit power from the stepper motor shaft to the camera. Movement of the gears during operation of the positioning device can generate a substantial amount of noise. This noise can be annoying and distracting to the conference participants. More importantly, the noise can interfere with acoustic localization techniques utilized to automatically orient the camera in the direction of the speaking participant.
Further, gears or other transmission elements may be susceptible to misalignment or breakage due to wear or rough handling, thereby rendering the positioning device partially or fully inoperative. Still further, the inclusion of the gear train into the positioning device makes its assembly more complex and consequently raises manufacturing costs. Finally, positioning devices utilizing stepper motors typically operate slowly and/or have limited angular resolution.
In view of the foregoing discussion, there is a need for a rotational positioning device which operates substantially noiselessly, does not require a gear train or similar to transmit power from the actuators to the camera.